Method of making a jointing piece



March 6, 1956 E. BOHNER ET AL 2,737,567

METHOD OF MAKING A JOINTING PIECE Filed May 51, 1952 United States Patent 7 METHOD OF MAKING A JOINTING PIECE Endre Bohner and Jzsef Lukcs, Budapest, Hungary, assignors to Licencia Talalmanyolcat Ertltesitii Vallalat, Budapest, Hungary, a firm Application May 31, 1952, Serial No. 291,454

4 Claims. (Cl. 219-) The present invention relates to a process of making a jointing piece for connecting light metal cables, such as aluminum cables to copper cables.

The invention has also special reference to joints for uniting bars, rods, wires and the like, which, on account of the nature of the materials of which they are composed, cannot readily be united by ordinary methods, such as soldering, brazing or welding.

The general object of the invention is to provide a strong and durable joint that can be readily and quickly made without the application of special means. More particularly the invention is intended for use in making integral electrical conductors from lengths of unlike conducting materials, such as copper on the one hand and a light metal such as aluminum or magnesium or their alloys on the other hand.

According to the invention the joint is made by means of a jointing piece comprising two parts one of which is made of copper, the other of a light metal, such as aluminum or magnesium or any alloy of one of these metals. These two parts are connected to one another by means of an interposed silver wafer with a thin layer of silver powder upon said silver wafer against which a body made of light metal is pressed. The electric resistance of said silver powder layer is the highest of the electric resistances of all the assembled bodies of the jointing piece. Then the two parts are subjected to a pressure of about 60-70 kg./cm. and simultaneously to a shock-like surge of electric current supplied by an electric transformer and having a density of about 6000 amp/cm. until bonding of said silver powder layer with the adjacent metal parts is completed.

The features of the invention will appear more fully from the following description, reference being made to the accompanying drawing, wherein a preferred form of the invention is shown. It is to be understood, however, that the drawing and description are illustrative only and are not to be taken as limiting the invention.

The figure in the drawing represents a perspective view of a jointing piece made by a process according to the invention.

Referring to this drawing, the jointing piece shown in the figure comprises two prismatic parts A and B, the part A of which is made of copper which may be readily welded to a copper conductor of nearly the same cross section as the part A. Part B is made of light metal such as aluminum or magnesium or an alloy of one of these metals and may be readily welded to a conductor of the same metal and approximately the same cross section.

The two parts A and B are connected to one another by means of a thin wafer C made of silver.

In order to connect the two parts A and B with the silver layer, we prefer to make use of a thin silver wafer which is about 1-3 mm. thick and is preferably made of contact-silver, i. e. a cold worked silver with less than 4% copper-content. This silver wafer or plate has the same cross-section as the bodies A and B and is con- 2,737,567 Patented Mar. 6, 1956 ICC nected to the copper body A in a known manner by means of hard-soldering. For this purpose any convenient silver-solder may be used together with an agent adapted to prevent oxydation, such as borate of sodium.

According to the invention the connection between the silver plate C and part B of aluminum is made by a welding process. In order to carry out this process a powder-layer is provided upon the free surface of the silver wafer, this layer consisting of pulverized silver. The silver powder-layer spread out upon the upper surface of the plate marked by the dotted line D in the drawing, may have a thickness of about 01-005 mm. As welding has to take place only in the Zone E between the silver plate and the part B of aluminum we apply a method by which heat will be localized mainly to this zone E. Since the electric resistance of the powderlayer is essentially greater than the electric resistance of the parts A, B and C, it is this layer that will be heated to the highest temperature when conducting an electric current of sufiicient density through the parts A, C and B. During this operation the parts A, C and B are pressed together by a force P of about 6070 kg./cm. We apply a shock-like rush of electric current of very high density and lasting only a few seconds. In this way the powder on the surface D, having the highest electric resistance of all parts concerned, is momentarily heated to a higher temperature than any other part of the piece,

so that melting and diitusing to the adjacent parts takes place in the zone E in a few seconds and practically without any heat-loss. The current carrying terminals are applied to the parts A and B, respectively, which are in a series connection with one another and the interposed plate C with the powder-layer. The shock-like rush of current, supplied by a transformer, has a density of about 6000 amp/cm. and is maintained for a time of about a few seconds. However, the density and the time duration of this rush of current depend upon the shape and area of the cross section of the parts of the jointing piece to be united. Since the pressure and the heat are applied simultaneously a welding takes place in the zone E dotted in the figure. Samples thus manufactured and subjected to bend-tests showed that the strength of the zone B comprising the welded connection was greater than the strength of the part B made of light metal.

The transformer used must be adapted to supply a heavy rush of current for a short period. Such transformers are well known in the art. When manufacturing great quantities of jointing pieces of the same shape and size, the pieces are subjected to rushes of current of the same intensity and the same duration. In order to control the current supply automatically in such cases, we preferably use a time switch provided in the secondary circuit of the transformer to switch off the current supply automatically after a predetermined period.

It has been found that in some cases there is no need to spread out a separate layer of pulverized silver on the surface of the plate C, and good results can be obtained by roughing the surface of the silver plate C by means of a file or the like. The granules, or at least part of them, produced by the filing operation remain embedded between the microscopic crests of the roughened surface thus forming an electric resistance great enough to cause a localized heating in the zone B with a temperature rise which, together with the simultaneous pressure, is sufiicient to cause welding of the two metals in this zone.

The cross section of the parts A and B may be of any desired shape such as polygonal, elliptical, circular or the like. This cross section is preferably the same as the cross section of the electric conductors to be connected to the jointing piece. The light metal conductor is preferably welded to the upper end of the light metal part B. The copper conductor may be connected to the part A in any desired manner by welding or by mechanical means or soldering or both.

The term unlike metals as used in this specification and appended claims includes copper and any light metal such as aluminum, magnesium or their alloys that cannot readily be united with copper by soldering or welding.

It is obvious, or" course, that the process is susceptible to the formation of bodies of complicated and irregular shape and for a variety of uses.

What we claim is:

1. The method of making a jointing piece for connecting light metal cables to copper cables comprising, making two bodies of approximately the same cross section, one of these bodies being of copper and the other being of the light metal to be joined to the copper; hard soldering a silver wafer to the copper body; providing a thin silver powder layer upon the free surface of the silver wafer; pressing the body of light metal against said silver powder layer; the density of the powder layer being selected to provide a higher electrical resistance per unit of depth than the electrical resistance per unit of depth of any of the thus assembled units; subjecting the assembly of the copper body, the silver wafer soldered to the copper body, the silver powder layer and the light metal body in a series arrangement to a pressure and while maintaining said pressure simultaneously passing a shocklike' surge of electricity supplied by an electric transformer through the series as embly until bonding of the silver powder layer with the adjacent metal parts is completed; and thereafter interrupting the current and releasing the pressure.

2. The method of making a jointing piece for connecting light metal cables to copper cables comprising, making two bodies of approximately the same cross section, one of these bodies being of copper and the other being of the light metal to be joined to the copper; hard soldering a silver wafer to the copper body; producing a thin silver powder layer upon the free surface of the silver water by roughening said surface; pressing the body of light metal against said silver powder layer; the density of the powder layer being selected to provide a higher electrical resistance per unit of depth than the electrical resistance per unit of depth of any of the thus assembled units; subjecting the assembly of the copper body, the silver wafer soldered to the copper body, the silver powder layer and the light metal body in a series arrangement to a pressure and while maintaining said pressure simul taneously passing a shock-like surge of electricity supplied by an electric transformer through the series assembly until bonding of the silver powder layer with the adjacent metal parts is completed; and thereafter interrupting the current and releasing the pressure.

3. The method of making a jointing piece for connecting light metal cables to copper cables comprising, making two bodies of approximately the same cross section, one of these bodies being of copper and the other being of the light metal to be joined to the copper; hard soldering a silver wafer to the copper body; spreading out a thin silver powder layer upon the free surface of the silver wafer; pressing the body of light metal against said silver powder layer; the density of the powder layer being selected to provide a higher electrical resistance per unit of depth than the electrical resistance per unit of depth of any of the thus assembled units; subjecting the assembly of the copper body, the silver wafer soldered to the copper body, the silver powder layer and the light metal body in a series arrangement to a pressure and while maintaining said pressure simultaneously passing a shockliite surge or" electricity supplied by an electric transformer through the series assembly until bonding of the silver powder layer with the adjacent metal parts is completed; and thereafter interrupting the current and releasing the pressure.

4. The method of making a jointing piece for connecting light metal cables to copper cables comprising, mak ing two bodies of approximately the same cross section, one of these bodies being of copper and the other being of the light metal to be joined to the copper; hard soldering a silver wafer to the copper body; providing a thin silver powder layer upon the free surface of the silver wafer; pressing the body of light metal against said silver powder layer; the density of the powder layer being selected to provide a higher electrical resistance per unit of depth than the electrical resistance per unit of depth of any of the thus assembled units; subjecting the assembly of the copper body, the silver wafer soldered to the copper body, the silver powder layer and the light metal body in a series arrangement to a pressure of about 60-70 kg./cm. and while maintaining said pressure simultaneously passing a shock-like surge of electricity having a density of about 6000 amp/cm. and supplied by an electric transformer through the series assembly until bonding of the silver powder layer with the adjacent metal parts is completed; and thereafter interrupting the current and releasing the pressure.

References Cited in the file of this patent UNITED STATES PATENTS 1,196,744 Chubb Aug. 29, 1916 2,100,258 Larson Nov. 23, 1937 2,372,607 Schwarzkopf Mar. 27, 1945 2,490,543 Robertson Dec. 6, 1949 2,513,365 Rogofi July 4, 1950 2,539,246 Hensel Jan. 23, 1951 2,539,247 Hensel Jan. 23, 1951 

